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Flexible piezoelectric sensors have attracted much attention due to good dynamic response, high sensitivity, and self-powered sensing advantages. However, piezoelectric outputs are usually affected by temperature variation, thus limit their applications on industrial intelligent equipment. Here, a new flexible piezoelectric sensor with in-situ temperature sensing and piezoelectricity calibration function is developed. The sensor can calibrate the piezoelectric output based on temperature to achieve high-accuracy sensing capability. It consists of a flexible polyimide substrate, S-shaped platinum interdigital electrodes and aligned piezoelectric fibers. The temperature sensor has a high sensitivity of 19.2 /C with good linearity, and keeps good accuracy under bending deformation. And when the working temperature range is 25-60C, the sensor has a good piezoelectricity calibration effect, so that it maintains a stable sensitivity of 244mV/without being affected by temperature. Furthermore, this paper systematically studied the influence of temperature on piezoelectric output, and established a calibration method to improve the accuracy of piezoelectric output under temperature changes. Finally, the flexible integrated sensor was conformably attached on the bearing surface to in-situ sensing temperature and vibration. The structural design and piezoelectricity calibration method can promote the application of flexible piezoelectric sensors in the industrial field.

The epidermal adhesive structure of many animals generates reliable adhesion on their engaged surfaces. However, current bio-inspired adhesion structures are difficult to function well in dry and underwater environments simultaneously. Interestingly, the male Dytiscus lapponicus attaches firmly to the rough shell of the female D. lapponicus in both dry and underwater conditions owing to the adhesive setae of its forelegs, and to the best of our knowledge, designing adhesive structures on multienvironments has never been reported. Here, a D. lapponicus-inspired adhesion structure (DIAS) is proposed and fabricated using double-exposure-fill molding technology accompanied with the material curing shrinkage, in which different structural features could be achieved by varying curing shrinkage ratios, elastic moduli, and back exposure time. The DIAS offered high, reversible, and repeatable strength in dry and underwater conditions with values of 205 and 133 kPa, respectively. By comparing the adhesion properties of different shapes via testing experiments and numerical analysis, a structural feature with an inclination of 15° was found to be optimal. Finally, the potential application of the DIAS in flexible electronic smart skin-attachable devices was demonstrated on a pig skin, paving the way for further bio-inspired adhesive designs for both dry and wet scenarios.

Non-planar morphology is a common feature of devices applied in various physical fields, such as light or fluid, which pose a great challenge for surface nano-patterning to improve their performance. The present study proposes a discretely-supported nanoimprint lithography (NIL) technique to fabricate nanostructures on the extremely non-planar surface, namely high-spatial-frequency stepped surface. The designed discretely imprinting template implanted a discretely-supported intermediate buffer layer made of sparse pillars arrays. This allowed the simultaneous generation of air-cushion-like buffer and reliable support to the thin structured layer in the template. The resulting low bending stiffness and distributed concentrated load of the template jointly overcome the contact difficulty with a stepped surface, and enable the template to encase the stepped protrusion as tight as possible. Based on the proposed discretely-supported NIL, nanostructures were fabricated on the luminous interface of light emitting diodes chips that covered with micrometer step electrodes pad. About 96% of the utilized indium tin oxide transparent current spreading layer surface on top of the light emitting diode (LED) chips was coated with nanoholes array, with an increase by more than 40% in the optical output power. The excellent ability of nanopatterning a non-planar substrate could potentially lead innovate design and development of high performance device based on discretely-supported NIL.

Metal mesh films as a kind of transparent conductive electrodes (TCEs) have shown high promise in various optoelectronic devices but are still challenged by a combination of high conductivity and transparency, mechanical robustness, and uniform electric field. Herein, we demonstrate a new concept of transparent and conductive films with a fully enclosed metal mesh, which is embedded in deep microcavities and is coated with a conductive polymer layer to combine these metrics. To ensure high conductivity and transparency, metal ink is filled into the fine (down to submicrometers) and deep mesh microcavities by electrowetting-assisted blading with low square resistances of 0.4 and 2.69 Ω sq-1 at typical transmittances of 76.9 and 87.4%, respectively. The covered thin conductive polymer layer improves the electric field uniformity of metal mesh films by at least three orders of magnitude. The fully enclosed metal mesh films exhibit excellent mechanical flexibility, indicated by the fact that the resistance is almost unchanged after 10,000 bending cycles at a bending radius of ∼5 mm. Based on the fully enclosed metal mesh films, the emission intensity of alternating current electroluminescent devices is improved by more than three times compared with that in the case of solely using common metal mesh films.

Liquid-crystal elastomer (LCE)-based soft robots and devices via an electrothermal effect under a low driving voltage have attracted a great deal of attention for their ability on generating larger stress, reversible deformation, and versatile actuation modes. However, electrothermal materials integrated with LCE easily induce the uncertainty of a soft actuator due to the non-uniformity on temperature distribution, inconstant resistance in the deformation process, and slow responsivity after voltage on/off. In this paper, a low-voltage-actuated soft artificial muscle based on LCE and a flexible electrothermal film is presented. At 6.5 V, a saturation temperature of 189 °C can be reached with a heating rate of 21 °C/s, which allows the soft artificial muscle quick and significant contraction and is suitable for untethered operation. Meanwhile, uniform temperature distribution and stable resistance of the flexible electrothermal film in the deformation process are obtained, leading to a work density of 9.97 kJ/m

In the areas of flexible displays and wearable devices, double-sided light-emitting devices have huge commercial applications. Here, we provide a novel form of flexible double-sided light-emitting devices by designing and manufacturing different transparent interdigital electrodes for lighting the structural areas of composite emitting layers. The transparent interdigital electrodes are fabricated by embedding multiwalled carbon nanotubes in interdigital mesh-structured microcavities using a doctor-blading process, and the emitting layers are fabricated by mixing copper-doped zinc sulfide (ZnS/Cu) phosphor particles with the transparent polydimethylsiloxane polymer. The fabricated double-sided light-emitting devices could be in the crimp state, exhibiting excellent flexibility. By designing the structure of the interdigital electrodes and the thickness of the emitting layers, the double-sided emission intensity of the light-emitting devices can be adjusted. Furthermore, based on the flexible double-sided light-emitting devices, various patterns can be successfully programed, such as the digital, grayscale, and ancient Chinese walls. The flexible and programmable double-sided light-emitting films provide a promising strategy for the next generation of customized flexible displays.

Micro-supercapacitors (MSCs) with thick interdigital microelectrodes of carbon-based materials exhibit excellent electrochemical performance and hold tremendous promise for applications in microscale energy storage devices. Here, a scalable strategy to fabricate thick embedded multiwalled carbon nanotubes (MWCNTs) as interdigital microelectrodes for MSCs has been developed and investigated. To this end, sufficient MWNCT inks are firstly cast onto pre-patterned microcavity surfaces and then more MWCNT materials are embedded into the microcavities by rapid solvent evaporation. After removal of residual materials from the surfaces by a doctor-blading process, thick interdigital MWCNT microelectrodes with heights up to 190 μm are obtained. These embedded microelectrodes simplify the device structure and improve the mechanical flexibility by acting as both active materials and current collectors. Using interdigital microelectrodes with a width of 250 μm and an interspace of 50 μm, the fabricated MSCs exhibit outstanding electrochemical performance with a high capacitance of 19.5 mF cm−2 and an energy density of 2.48 μW h cm−2 at a power density of 24.7 μW cm−2. On the other hand, four light emitting diodes (LEDs) are successfully powered by three series of MSCs, indicating that MSCs can be connected in series and parallel to yield suitable operating voltages and currents for practical applications.

Hydrogen sensor based on Pd nanogap arrays was fabricated using the swelling induced cracking method. The square hole Pd array is patterned on the polymer to define the position of the nanogaps. We discuss the influence of the size and the shape of the holes on the formed nanogaps. The structural and morphological characteristics of the metal array and the nanogaps were investigated using laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). To illustrate an application of the nanogap structure, the Pd nanogap array was deposited on epoxy and polyimide (PI) substrate and used as H2 sensor, showing a good sensitivity and stability at room temperature. Moreover, the performance of the nanogap array on PI substrate remains stable after annealing at 80–180 °C. This effect is attributed to the high thermal stability of the PI substrate. The effective fabrication method, good sensitivity and the high stability of the Pd nanogap arrays show promising application for H2 sensing.

Improving the triboelectrification effect between tribo-materials is fundamentally important for advancing the booming community of triboelectric nanogenerators (TENGs) and self-powered sensors. Microstructures played key roles in improving the triboelectrification effect, however, the uprightness of commonly used microstructures always limited the triboelectrification to interfaces between the tops of microstructures and opposite tribo-films during vertical contact/separation processes. In this study, bendable and slidable fish-scale-like microstructures were developed to surpass the limitations by extending the triboelectric interfaces from their tops to their sidewalls, taking the advantages of bending and sliding movements. Based on the fish-scale-like microstructures, the as-prepared TENGs delivered open-circuit voltages reaching up to 470 V and a short-circuit current density of 45 μA/cm 2 . These values were two-fold higher than those obtained with vertical microstructures under the same testing conditions. The as-assembled self-powered pressure sensors based on fish-scale-like microstructures delivered linear measurement ranges reaching up to 42 kPa, low detection limit of 10 mPa, high sensitivity of 1.03 mV/Pa, and ultrafast response of 0.1 ms. These features were significantly enhanced when compared to those of vertical microstructures. More importantly, we also developed a straightforward and low-cost duplication method for fabricating the fish-scale-like microstructures, which are easily achievable for fabricating the high-performance TENGs or self-powered pressure sensors.

We present a tiling light sheet microscope compatible with all tissue clearing methods for rapid multicolor 3D imaging of centimeter-scale cleared tissues with micron-scale (4×4×10 μm3) to nanometer-scale (70×70×200 nm3) spatial resolution. The microscope uses tiling light sheets to achieve a more advanced multicolor 3D imaging ability than conventional light sheet microscopes. The illumination light is phase modulated to adjust the 3D imaging ability of the microscope based on the tissue size and the desired spatial resolution and imaging speed, and also to keep the microscope aligned. The ability of the microscope to align via phase modulation alone also makes the microscope reliable and easy to operate. Here we describe the working principle and design of the microscope. We demonstrate its imaging ability by imaging various cleared tissues prepared by different tissue clearing and tissue expansion techniques.

Coating hierarchical micro-nanostructures on the surface of optoelectronic devices has been demonstrated to improve the overall performance. However, fabricating desired structures on a fragile optoelectronic device substrate is still challenging. A suspended-template electric-assisted nanoimprinting technique is proposed herein to controllably fabricate hierarchical micro-nanostructures on a fragile substrate. The suspension design of the template ensures that it conveniently deforms to fully fit the surface fluctuation of the substrate. The deformation of template and the filling of liquid polymer in the micro/nanocavities of the template are both driven by the powerful surface/interface force generated by an electric field applied between the template and substrate surface, thus protecting the fragile substrate from squeezing damage. Different morphologies of hierarchical micro-nanostructures are fabricated by changing the electric field. Based on suspended-template electric-assisted nanoimprinting, the environmentally adaptable fully covering hierarchical micro-nanostructures are encapsulated on the surface of flip-film light-emitting diode chips, thus significantly enhancing their light management in complex environments.

Microsupercapacitors (MSCs) are vital power sources for internet of things (IoTs) and miniaturized electronics. The performance of MSCs is often restricted by its low areal energy density, which is due to the low areal mass loading of active materials. Constructing thick planar microelectrode with fine structure and high aspect ratio is an efficient way to increase mass loading, but limited by the breakable nature of porous electrode materials. Here, it is found that the mechanical and electrical properties of porous electrodes, as well as their surface area utilization and internal ion diffusion pathway, can be synergistically tuned by infilling gel electrolyte into internal pores of porous electrode films. The tuned thick porous electrode films are robust enough to enable laser ablation of three dimensional (3D) microelectrodes for high mass loading and high aspect ratio. The areal capacitance of 3D microelectrodes is able to increase linearly with mass loading (or thickness) up to at least 13 mg cm−2 (or 260 µm) for a value of up to 4640 mF cm−2 based on active carbon. The 3D MSCs deliver areal energy density of 1318 μWh cm−2, which is comparable to the best of Li‐ion 3D microbatteries while exhibiting superior electrochemical and mechanical stability., The mechanical and electrical properties of thick electrode films are tuned by infilling gel electrolyte, enabling laser ablation of 3D microsupercapacitors (MSCs) with high mass loading and high aspect ratio. The MSCs deliver an energy density of 1318 μWh cm−2, comparable to the best of microbatteries while exhibiting a superior power density of 102 mW cm−2 with high mechanical and cycling stability.

Polarized radiative luminous semiconductor chips have huge application potential in many highly value-added fields. The integration of a subwavelength grating is recognized to be the most promising method for the development of polarized chips, but still faces the challenge of low polarized radiative performance. This paper describes a proposal for, and the development of, a scattering-induced enhanced-polarization light-emitting diode chip by directly nanoimprinting a metal-containing nanoparticle-doped grating onto the top surface of a common flip chip. The rate at which quantum-well light emission is used by the developed polarized chip is improved by more than 30%. More attractively, the doped scattering nanoparticles function as a scattering-induced polarization state converter that is sandwiched in between the top aluminum grating and the bottom silver reflector of the chips. The originally non-radiated light, with an electric-field vector parallel to the grating lines, is reflected back and forth inside the sandwich until it changes to the perpendicular vibration mode and is radiated outside the chip. Therefore, the polarization extinction ratio is greatly improved, compared to undoped samples.

In this work, we focus on frequency-dependence of pearl chain formations (PCF) of gold nanoparticles driven by AC dielectrophoresis (DEP), especially in a low field-frequency range, where induced double-layer charging effect at ideally polarizable surfaces on particle DEP behavior and surrounding liquid motion need not be negligible. As field frequency varies, grown features of DEP assembly structures ranging from low-frequency non-bridged gap to high-frequency single gold nanoparticle-made nanowires bridging the electrodes are demonstrated experimentally. Specifically, at 10 kHz, a kind of novel channel-like structure with parallel opposing banks is formed at the center of interelectrode gap. In stark contrast, at 1 MHz, thin PCF with diameter of 100 nm is created along the shortest distance of the isolation spacing. Moreover, a particular conductive path of nanoparticle chains is produced at 1 MHz in a DEP device embedded with multiple floating electrodes. A theoretical framework taking into account field-induced double-layer polarization at both the particle/electrolyte and electrode/electrolyte interface is developed to correlate these experimental observations with induced-charge electrokinetic (ICEK) phenomenon. And a RC circuit model is helpful in accounting for the formation of this particular non-bridged channel-like structure induced by a low-frequency AC voltage. As compared to thin PCF formed at high field frequency that effectively short circuits the electrode pair, though it is difficult for complete PCF bridging to occur at low frequency, the non-bridged conducting microstructure has potential to further miniaturize the size of electrode gap fabricated by standard micromachining process and may find useful application in biochemical sensing.

A stable and uniform electric field is to be generated even though a large mechanical deformation is the primary criterion for a transparent conductive film. This study proposes a protective integrated transparent conductive film (PITCF) including indium tin oxide (ITO), a silver nanowire (Ag NW) network, and a protective polydimethylsiloxane (PDMS) layer. A firmly bonding process of ITO/Ag NW/PDMS is established to avoid the failure of Ag NW to be oxidized by interlayer residual air or wrapped by liquid PDMS. Besides the good optical transparency, haze, and electrical conductivity as the only ITO film, the developed PITCF exhibits excellent bending resistance and mechanical stability. The ITO rupture fragments after bending deformation are firmly interconnected by the constrained Ag NWs. Even though the PITCF is bended more than 1000 cycles at a 6.5 mm bending distance, the changes in electrical resistance of PITCF are below 9.7%. Finally, an electroluminescent device with high bending resistance and uniform and high luminance is developed based on the designed PITCF.

During research on the propeller−ice contact process, it was found that there is a shadowing effect that has a significant influence on the propeller loading. The shadowing effect was observed to occur with both staggered configurations of multi-propellers along with the separate blades of single propellers. The shadowing effect causes the load from the ice to decrease on the aft propellers or a following blade compared to the blade currently in contact with the ice. Two numerical simulation models based on the peridynamics method have been established in order to study shadowing effect for both forward and aft multi propeller-ice configurations as well as individual blades of a single propeller. The influence mechanism of the shadowing effect on the sea ice failure mode along with the loads acting on the propellers are examined in this paper. Additionally, a new analytical shadowing effect coefficient on the ratio of the front and back contacts divided by the axial length of the damaged ice is put forward based. The results show that the shadowing effects are well modeled by both peridynamic numerical simulations and the analytical shadowing coefficient.

This paper proposes a novel method of multibeam laser heterodyne measurement for an electrostriction coefficient. Based on the Doppler effect and heterodyne technology, loaded with the information of length variation to the frequency difference of the multibeam laser heterodyne signal by the frequency modulation of the oscillating mirror, this method can obtain many values of length variation caused by different voltages after the multibeam laser heterodyne signal demodulation simultaneously. Processing these values by a weighted-average method, it can obtain length variation accurately, and eventually obtain value of electrostriction coefficient of metal by the calculation. This novel method is used to simulate measurement for electrostriction coefficient of PZT under different voltages by MATLAB, and the obtained result shows that the relative measurement error of this method is just 0.98%.

Subsurface damages produced in grinding process will influence optical performance and lifetime of optical elements.The testing for subsurface damage of polished surface is research hot and difficult point now.Combination of confocal image,tomography technology,microscope optics,optical scatter and weak signal processing,a novel method based on laser confocal microscope tomography is proposed.The effects of different sizes of pinhole on measure accuracy are analyzed,and the cross section microstructure picture of the subsurface damage sample is given.The subsurface damage depth is about 45 μm with this novel method.For the same K9 glass,the subsurface damage depth is about 50～55 μm with the chemical corrosion treatment technology.The measurement results are basically consistent.Comparison with the destructive etching method shows that this novel method is good for polished surface in quantitative and non-destructive.

Large-area nanostructures are widely used in various fields, but fabrication on large-area uneven substrates poses a significant challenge. This study demonstrates a step-controllable electric-field-assisted nanoimprint lithography (e-NIL) method that can achieve conformal contact with uneven substrates for high fidelity nanostructuring. Experiments are used to demonstrate the method where a substrate coated with liquid resist is brought into contact with a flexible template driven by the applied electric field. Theoretical analysis based on the elasticity theory and electro-hydrodynamic theory is carried out. Effective voltage range and the saturation voltage are also discussed. A step-controllable release of flexible template is proposed and demonstrated to ensure the continuous contact between the template and an uneven substrate. This prevents formation of air traps and allows large area conformal contact to be achieved. A combination of Vacuum-electric field assisted step-controllable e-NIL is implemented in the developed prototype. Finally, photonic crystal nanostructures are successfully fabricated on a 4 in., 158 μm bow gallium nitride light-emitting diode epitaxial wafer using the proposed method, which enhance the light extraction property.

This letter proposes a surface-energy driven process for economically creating polymer microlens array (MLA) with well controllable curvatures. When a UV-curable prepolymer flows into a cell constructed by multiple holes on a top template and a flat substrate, since the edge pinning of the contact line, an array of curved air/prepolymer interface forms around each microhole of the template. Then a UV-radiation of the bulk prepolymer leads to a solid microlens array. The curvature of the air/prepolymer interface can be controlled by choosing materials with different interface free energy or varying the gap height mechanically.

As a widely applicable process for fabricating micro- or nanostructures, micromolding in atmosphere would require the removal or minimization of air-trapping in mold cavities so as to fill the liquid prepolymer fully into the mold for generating an exact polymer duplicate. This has been difficult, if not impossible, especially for a mold with high aspect ratio, varying size/shape, or isolated cavities because the air can be trapped inside such mold cavities in most variants of the molding process. This paper presents an electrowetting assisted transfer micromolding process to solve this problem. A feeding blade continuously supplies a UV-curable prepolymer over a dielectric-coated conductive mold placed on a progressively advancing stage. A voltage applied to the electrode pair composed of the feeding blade and mold generates an electrowetting of the prepolymer to the mold. The electrowetting allows for the three-phase contact line to pass progressively along the sidewalls and bottoms of the cavities, completely pushing out the air initially occupying the cavities, or generates an electrocapillary force large enough to pull the prepolymer deeply into the mold by compressing the air already trapped inside the cavities to a minimized volume. An experiment has been performed for micromolding with deep cavities of various shapes and sizes, demonstrating an essential improvement in the structural integrity of the polymer duplicates.

High-efficiency organic light-emitting diodes (OLEDs) have generated tremendous research interest. One of the exciting possibilities of OLEDs is the use of flexible plastic substrates, which unfortunately have a mismatching refractive index compared with the conventional ITO anode and the air. To unlock the light loss on flexible plastic, we report a high-efficiency flexible OLED directly fabricated on a double-sided nanotextured polycarbonate substrate by thermal nanoimprint lithography. The template for the nanoimprint process is a replicate from a silica arrayed with nanopillars and fabricated by ICP etching through a SiO2 colloidal spheres mask. It has been shown that with the internal quasi-periodical scattering gratings the efficiency enhancement can reach 50% for a green light OLED, and with an external antireflection structure, the normal transmittance is increased from 89% to 94% for paraboloid-like pillars. The OLED directly fabricated on the double-sided nanotextured polycarbonate substrate has reached an enhancing factor of ∼2.8 for the current efficiency.

Traveling-wave electroosmotic (TWEO) pumping arises from the action of an imposed traveling-wave (TW) electric field on its own induced charge in the diffuse double layer, which is formed on top of an electrode array immersed in electrolyte solutions. Such a traveling field can be merely realized in practice by a discrete electrode array upon which the corresponding voltages of correct phase are imposed. By employing the theory of linear and weakly nonlinear double-layer charging dynamics, a physical model incorporating both the nonlinear surface capacitance of diffuse layer and Faradaic current injection is developed herein in order to quantify the changes in TWEO pumping performance from a single-mode TW to discrete electrode configuration. Benefiting from the linear analysis, we investigate the influence of using discrete electrode array to create the TW signal on the resulting fluid motion, and several approaches are suggested to improve the pumping performance. In the nonlinear regime, our full numerical analysis considering the intervening isolation spacing indicates that a practical four-phase discrete electrode configuration of equal electrode and gap width exhibits stronger nonlinearity than expected from the idealized pump applied with a single-mode TW in terms of voltage-dependence of the ideal pumping frequency and peak flow rate, though it has a much lower pumping performance. For model validation, pumping of electrolytes by TWEO is achieved over a confocal spiral four-phase electrode array covered by an insulating microchannel; measurement of flow velocity indicates the modified nonlinear theory considering moderate Faradaic conductance is indeed a more accurate physical description of TWEO. These results offer useful guidelines for designing high-performance TWEO microfluidic pumps with discrete electrode array.